Regular casting methods such as conventional die casting, gravity permanent mold casting, and squeeze casting have long been used for metals and their alloys. However, these current processes when used to manufacture parts with relatively complex geometries often yield products with undesirable shrink porosity, which can adversely impact the quality and integrity of the part. Shrink porosity defines a condition that arises as a metal part begins to shrink as it cools and solidifies along the outer surface, leaving pockets of air (referred to as “voids”) trapped in the center of the part. If the voids are not reconstituted with metal, the cast part is termed “porous.” Particularly in the design of complex parts, such as, for example, automotive transmission valve bodies or engine bedplates, the greatest shrink porosity is found in the thicker areas.
One method of reducing shrink porosity is to cast semi-solid metal (SSM) instead of liquid molten metal. SSM casting, which generally involves low temperature, low velocity, and less turbulent injection of metal, typically reduces the occurrence of shrink porosity. Where SSM casting of metal materials has been involved however, the conventional methods have not been employed successfully to date. Rheocasting and thixocasting are casting methods that were developed in an attempt to convert conventional casting means to SSM casting, but these SSM methods require costly retrofitting to conventional casting machinery and attempts at conventional casting of SSM have been unsuccessful.
Another method to reduce porosity levels is to apply a direct-feed system. The direct-feed system allows molten metal to continue to feed directly into the areas of thick geometry during solidification, thereby filling the air pockets with metal as they form. In this way, shrink porosity can be significantly reduced in those areas. Preferably, the direct feed can be localized to multiple areas within particularly complex parts or as required.
Accordingly, it is desirable to provide a method of casting SSM metals and molten metals and alloys utilizing conventional and/or rheocasting die casting devices that can impart desirable mechanical properties. It is further desirable to provide a process to control the shrink porosity of cast parts at multiple locations throughout a part. Further still, it is desirable to provide a method of producing products with metal alloy castings wherein the temperature of the semi-solid metal slurry and molten metal can be controlled.